DESCRIPTION: The long term interest of this research program is in understanding the regulation of the nitric oxide (NO) signaling pathway as it relates to pulmonary vascular physiology and pathophysiology. This proposal will define the molecular mechanisms by which chronic hypoxia up-regulates inducible and endothelial NOS (eNOS and iNOS) and investigate the role of this up-regulated NO in the lung vascular remodeling process. Specific Aim 1 will address the hypothesis that chronic hypoxia up-regulates iNOS primarily via hypoxia inducible factor 1 (HIF-1) by 1) further defining the transcriptional regulation of iNOS by HIF-1 and identifying other factors that enhance or attenuate this response; 2) determining that HIF-1 and other factors shown to mediate hypoxia-induced up-regulation of iNOS in in vitro studies are relevant to the in vivo chronic hypoxia induced pulmonary hypertension model, and 3) determining the mechanisms of human iNOS regulation by hypoxia. Specific Aim 2 will address the hypothesis that hypoxia up-regulates eNOS secondary to transcriptional and post-transcriptional regulation of eNOS by hypoxia and by these secondary agents which increase during chronic hypoxia; 2) by determining if post-transcriptional effects are also involved; and 3) defining the in vivo correlates of these observations. Specific Aim 3 will address the hypothesis that NO modulates the pulmonary vascular remodeling which occurs with chronic hypoxia-induced pulmonary hypertension by assessing changes in vascular remodeling, VSM proliferation and apoptosis in the chronic hypoxia model following inhibition or enhancement of the NO pathway, in NOS knockout mice and in a lung organ culture model. Specific Aim 4 will address the hypothesis that NOS isoforms and NO activity are up-regulated in human pulmonary hypertension by evaluating the expression and activity of NOS isoforms and guanylyl cyclase in surgical lung specimens from patients with pulmonary hypertension. These studies should answer important questions concerning the molecular mechanisms by which eNOS and iNOS are up-regulated in pulmonary hypertension, and may lead to new therapeutic strategies.